Such a fuel injection device is generally known in the prior art. For example, an injection system for LPG is being marketed by Applicant under the name of LPI. The LPG in this case is in a liquid state during the injection and is not converted to vapour form until it is in the intake duct. Such a system has many advantages, such as negligible loss of power compared with petrol as the fuel, accurate metering possibilities and simple connection to electronics of electrically controlled petrol injection systems.
In order to ensure that the LPG used remains in the liquid state, a pump for increasing the pressure is used. Numerous measures are also taken to prevent heat transfer as much as possible from parts of the internal combustion engine to the supply/discharge pipes or injectors. The result of this is that liquid LPG can be guaranteed to be present in the injectors in all operating circumstances.
It has been found that injectors used inevitably show some leakage. This means that after the internal combustion engine has been switched off fuel goes into the intake manifold and makes starting more difficult. For the first part of the mixture which has been drawn in will contain excess fuel and ignite poorly, which gives rise to a risk of the spark plugs becoming fouled. This problem is particularly prevalent if the starting-up is on petrol. For during the first starting revolutions an excess of a mixture of vaporized LPG and petrol will be present, with the result that the petrol could well become deposited on the electrodes of the spark plugs.
This effect is a particular nuisance if the internal combustion engine is started up again a short time after being switched off. For if a longer period is allowed to elapse, the gaseous LPG will leak out of the system through the outlet or through other cylinders.
European Application 0,178,484 discloses an internal combustion engine which can run both on gas and on petrol. In this case LPG is introduced into the internal combustion engine in the liquid state.
U.S. Pat. No. 5,159,915 discloses an injector provided with a heating element. This injector is designed exclusively for running on petrol.